Method and apparatus for the production of coated tablets



June 11, 1957 c. F. WHITE 2,795,199

METHOD AND APPARATUS FOR THE PRODUCTION OF COATED TABLETS Filed Sept. 27, 1954 2 Shets-Sheet 1 E $2 I 5 I E m a) \E m INVENTOR CAM/e Fl hnig -b l7 ltg June 11, 1957 c, wHlTE 2,795,199

I METHOD AND APPARATUS FOR THE PRODUCTION OF COATED TABLET S Filed Sept. 2'7, 1954 I 2 Sheets-Sheet 2 F I G. 2

INVENTOR char/es Fl gml'nlg AIt ATTO'R EIY METHODJAND APPARATUS FOR-THE PRODUC- TION F. COA'IZED TABLETS This inventiomrelatesto:tl1'e= production of coated tablets.- The -term-tab1etsas used hereinafterincludesa pills and similar objects; s

It is known to produce coated tablets-for: medicinal purposes by compressing a powdered coating material (which expression 2 includes granulated:coatingzinaterial) preferably asugar.coating,materia l,.around a core tablet, 1

this operation usually being calledpress coating. Such tablets are 1 usually madein-rotarytablet presses of. the kind which includearotatabledie. plate having upper and lower punches which are rotatable with the die plate and r w tures Each-z,

are reciprocable in --dieapertures in the die plate: Int order to produce a coated tablet, a layer of powdered coating material is inserted in each die aperture on top of the lower punch therein. A core tablet is then inserted in the aperture on top of the layer of coating material and a second layer of coating material is fed on top of the core tablet. The core tablet and the two layers of powdered material are then compressed between the upper and lower punches to produce the coated tablet. If tablets are to be produced successfully in this way, it is important to position the core tablet centrally within its coating (i. e. to centre the core tablet), but difiiculty has always been experienced in doing this.

It is an object of the present invention to provide a more simple and effective way of positioning a core tablet centrally within its coating than has hitherto been proposed.

Many unsuccessful attempts have previously been made to solve the problem of centering core tablets during a press-coating operation. One proposal is made in the specification of German Patent No. 475,093 which describes a machine including a rotatable die plate having a circular series of die apertures in each of which a pair of punches can reciprocate. A core tablet is inserted into a die aperture on to a layer of powdered coating material on top of a lower punch and a co-operating upper punch which has a concave working surface is guided in a cam track so as to bear lightly on the core tablet: this is alleged to centre the core tablet, but I have found that it does not, in fact, do so satisfactorily.

I have made the surprising discovery that a core tablet can be satisfactorily centered if an upper punch having a concave working surface is allowed to fall freely on to the core tablet.

Accordingly, the present invention provides a method of producing coated tablets in which a first layer of powdered coating material is placed on a lower punch in a die aperture, a core tablet is placed on the said layer, an upper punch having a concave working surface is allowed to fall freely on to the core tablet thereby to centralise the core tablet, the upper punch being then withdrawn from the core tablet and a second layer of coating material being fed into the die aperture on top of the core tablet, and the whole being then compressed between the upper and lower punches to produce the Coated tablet.

The invention also provides a press-coating apparatus "ice comprising; a-rotatable die plate having a circular row of dieapertures-andmpper' and. lowerpunches which .run in cam: tracks-so as to be .reciprocated 'in' the. die apertures as thediewplate rotates wherein -the upper puncheszhave concave working surfaces" and run in z a 1 cam track which is interrupted so that each punch in turn. can fall Y freely in: a co-operating; die: aperture, thereby *to position a a core tablet therein and can then re-enter the camtrackg:

A=-. preferred: embodimentof ,the invention is illustrated in the accompanying;v diagrammatic. drawings in which:

Figure l is a-developed view illustrating the positions occupied by a pairof punchesrduring one-cycleof revolutionof a-press-coatingimachine;

Figures .2. and 3"aressec,tional views respectively illustratingza core tablet in atdie aperture. before; and afterit has-been-correetly; positioned, v

Figure 4 is an elevation of theupper-part ofa presscoating machine, while Figure; 5- is; aqfragmentary plan view-of: the same machine. I

As shown inI-thedrawings; aco'ating; ofa powdered materialcan gbez;compressed: -around, a=-core tabletil (Figures; 2' and --3 in a :pressacoatingrzmachine: comprising aaxrot-atable'idie:.prate:2 having a: circulamrow': of die 'aperie aperture 3 c amreceive an upper-punch 4 and a lower punch 5 which have concave working surfaces 6, 7 and heads 8, 9 respectively guided in upper and lower cam tracks 10, 11 so that they are caused to move to and from each other as the die plate 2 rotates. Except for the novel way of controlling movement of the upper punches 4 to be hereinafter described, this arrangement is generally known and need not be described in greater detail.

A first or lower layer of powdered coating material 12 is fed through a chute 13 or by other suitable means on to the top of each lower punch 5 as each die aperture arrives in turn at a first filling station A (Figure l). The die plate continues to rotate and a core tablet 1 is inserted into a die aperture on top of the firs-t coating layer at a station B, the insertion preferably being efiected by a rotatable feed plate 14 having a circular row of apertures 15 which register with the die apertures 3 as the plates 2 and 14 rotate and each of which is loaded with a core tablet in any suitable way. At this stage the core tablet 1 is not necessarily centrally positioned in its die aperture 3 and may for example occupy the position shown in Figure 2. Immediately after the core tablet 1 has been inserted in the aperture 3, the upper punch 4 which co-operates with the die aperture is (at station C) allowed to fall freely on to the core tablet from the cam track 10 controlling the punch. Owing to the concavity of the upper punch 4 and the fact that the core tablet 1 is resting lightly on top of the first layer 12 of coating material, the core tablet 1 is positioned centrally in the die aperture when it is struck by the concave surface of the upper punch 4 as shown in Figure 3. The upper punch is then raised by the cam track 10 to permit a second layer of coating material (not shown) to be fed through a chute 16 or other suitable feed device on top of the core tablet as the die aperture passes station D. The whole is then compressed in the usual manner at a compression station E, the upper and lower punches being loaded in the usual manner by being passed between a pair of rollers 17 bearing on the upper and lower punches. The upper and lower punches then both rise to permit the finished tablet to be raised clear of the die aperture "at a station F.

In order to allow the upper punches 4 to fall freely on to core tablets when the punches pass the station C, the upper cam track 10 is interrupted at 18 as shown in Figures 1 and 4: the upper punches can re-enter the cam I traclr 10 immediately after they have fallen on to the core tablets. It is essential that nothing shall impede the free fall of the punches at the station C as otherwise the tablets will not be satisfactorily centered at commercially dcsirable speeds. For this reason, the upper punches 4 must be a free sliding fit and not a tight fit in their punch holder 19. Moreover, it is desirable to use the upper punches in a dry condition, i. e. clean and free from any lubricant; if for any reason it is considered necessary to lubricate the punches, the lubrication should be effected by wiping them with a cloth charged with a very light oil before insertion into the punch holder 19, the merest smear of oil being applied to each punch. If the upper punches are at this station C allowed lightly to bear on the core tablets (as is proposed in the aforesaid German patent specification No. 475,093) the core tablets will not be properly positioned.

The core tabletsl can be of conventional shape, i. e. be cylindrical with convex ends, or they can be spherical or they can have a hole through which a stem of coating material can be pressed to form a bond between the upper and lower surfaces of the outer coating so "as to avoid any tendency to capping.

What I claim is:

l. A method of producing a coated tablet comprising the steps of feeding a first layer of powdered coating material into a die aperture on top of a lower punch therein, feeding a core tablet into said die aperture on top of said first layer, allowing an upper punch having a concave working surface to fall freely on to said core tablet thereby to centralise said tablet, withdrawing said I upper punch from said core tablet, feeding a second layer of powdered coating material into said die aperture on top of said core tablet, and compressing the whole between said punches to produce said coated tablet.

2. Apparatus for the press coating of tablets comprising a rotatable die plate having a circular series of vertical die apertures therein, a lower punch movable in each die aperture, a lower cam track in which said lower punches run as said die plate rotates whereby said punches are raised and lowered in said apertures, means for feeding a first layer of powdered material on to each lower punch in turn, means for feeding a core tablet on top of each first layer of powdered material in turn, means for feeding a second layer of powdered material on top of each core tablet in turn, an upper punch movable in each die aperture, and an upper cam track in which said upper punches run as said die plate rotates thereby to compress said powdered material around said core, said upper cam track being interrupted to allow each said upper punch to UNITED STATES PATENTS 1,248,571 Stokes Dec. 4, 1917 FOREIGN PATENTS 475,093 Germany Apr. 17, 1929 

